More than hundred years ago Einstein and de Haas performed a pioneering experiment to demonstrate the transfer of quantum to mechanical angular momentum in a ferromagnetic material. The experiment, which has since come to be known as the Einstein-de Haas (EdH) effect, is an elegant demonstration of angular momentum conservation. Fast forward, hundred years later we can now add another exciting ingredient to the mix - topology. This abstract mathematical concept manifests itself as edge states of topological magnon excitations in magnetic materials, for example in CrI3 or Lu2V2O7. Since, topological magnons possess angular momentum of revolution (motion around sample edge) and rotational angular momentum (of the magnon wave packet), one can imagine generalizing the EdH effect to include transfer of angular momentum from these novel topological excitations to the bulk material itself. In this talk, I will discuss our prediction of the Einstein-de Haas effect in topological magnon insulators. Temperature variation of angular momentum in the topological state shows a sign change behavior, akin to the low temperature thermal Hall conductance response. This manifests itself as a macroscopic mechanical rotation of the material hosting topological magnons. We show that an experimentally observable Einstein-de Haas effect can be measured in the square-octagon, the kagome, and the honeycomb lattices. Albeit, the effect is the strongest in the square-octagon lattice. We treat both the low and the high temperature phases using spin wave and Schwinger boson theory, respectively. We propose an experimental set up to detect our theoretical predictions. We suggest candidate square-octagon materials where our theory can be tested [1].
[1] Einstein-de Haas effect of Topological Magnons, Jun Li, Trinanjan Datta, Dao-Xin Yao, arXiv:2005.10273 (2020)
Grant Acknowledgement:
Sun Yat-sen University Grant No. OEMT-2017-KF-06 and OEMT-2019-KF-04
Department of Chemistry and Physics, Augusta University
Trinanjan Datta is a Professor of Physics in the Department of Chemistry and Physics at Augusta University, Augusta, GA. He obtained his B.S in Physics from the University of Calcutta (St. Xavier’s College, Kolkata, India), M.S. from the Indian Institute of Technology (Kanpur, India), and his doctoral degree in theoretical condensed matter physics from Purdue University (West Lafayette, IN, USA). His research interests include theoretical and computational studies of magnetic systems and the scholarship of teaching and learning (SoTL). He has published numerous research articles on magnetism and delivered several invited national and international research presentations. His research has been funded by the National Science Foundation, Cottrell Research Corporation, and State Key Laboratory of Optoelectronics at Sun Yat-Sen University (China). Dr. Datta actively mentors undergraduate research students at Augusta University and masters and doctoral students at Sun Yat-Sen University. He has co-authored a textbook titled Introductory Solid State Physics with MATLAB Applications. He is the recipient of the Augusta State University Louis K. Bell Alumni Research Award, the Kavli Institute for Theoretical Physics (KITP) scholar award, Augusta University College of Science and Mathematics Excellence in Research Award, the University System of Georgia SoTL fellowship, and Augusta University Individual Teaching Excellence Award. He is an Anacapa Scholar of the Anacapa Society and a member of the American Physical Society.
Venue: TDLI Meeting Room 202
